Vehicles such as forklifts, utility carts, golf carts and other electric vehicles are known to use a variety of controls for operating, accelerating and/or braking functions of the electric drive system. For example, it is known to use various types of position sensors, both mechanical and optical, to determine the position of an accelerator pedal and to control acceleration accordingly. Electromechanical potentiometers use a resistive element that is swept by a contacting member. The contacting member moves with the foot pedal or other similar actuation system. As the contacting member moves across the resistive element, the voltage changes across the device, causing the output voltage of the device to vary with pedal position. Another known system uses a magnetic field to change the state of a solid state element. As the magnet moves past the device, the state of electronics within the device changes, indicating that the pedal or other actuator has moved. Known as “Hall Effect” devices, some read the change in the magnetic field and interpret the change like a potentiometer, varying the output voltage with the change in magnetic field polarity and amplitude.
Electromechanical systems have limited life due to mechanical wear. Since such devices depend on two surfaces contacting and wiping against one another, friction and debris can cause the materials to wear and the potentiometer to fail prematurely. Wear is accelerated if the components are not aligned properly. Misalignment of components can occur quickly and unexpectedly because of the sometimes rugged use to which the vehicles are exposed. Significant wear can occur before the misalignment is detected during routine inspections or maintenance.
Hall Effect devices and some optical systems have high manufacturing costs in addition to mechanical limitations. Hall Effect devices require microchips that are specially provided to work with the Hall Effect, and can add considerable cost to the device. Optical devices often require an encoder disk with precisely located and etched markings that can be read by optical elements. Often the disks are laser etched and expensive. The optical devices can be very sensitive to contaminants that change the optical properties of the disk. Sealing the device may be effective in avoiding contamination, but adds further cost to the assembly.
Acoustic wave sensors and switches are known in which a transducer is mounted on or adjacent to an acoustic wave cavity formed in a substrate to generate an acoustic wave that is a standing wave trapped in the acoustic wave cavity. These acoustic wave sensors or switches have been used to detect a touch on a surface of the substrate opposite from the surface on which the transducer is mounted by sensing changes in the standing wave.
There is a need for durable, yet accurate controls for electric vehicles that can be provided at reasonable expense.